The present invention relates to boron nitride containing titanium nitride which are produced by a vapor deposition technique and a method of producing them.
The present invention is further directed to BN type composite ceramics produced from the boron nitride.
Boron nitride (BN) is superior in high temperature stability, chemical stability and electric insulating property. Particulary hexagonal type BN has a useful anisotropy in thermal conductivity in addition to the foregoing superiority and thus the anisotropic boron nitride has been extensively used as useful materials for various kinds of crucibles, heat insulators and wave guide for microwave, etc.
Particulaly, boron nitride (BN) produced by means of chemical vapor deposition is evaluated as a high quality BN because it is highly pure and free from contamination and great developments in its use are taking place. On the other hand, massive body of boron nitride has been produced by adding boric acid or silica glass as sintering assistant agent to powdered boron nitride and then sintering under atmospheric pressure or hot press sintering. The sintered body thus produced is quite different from boron nitride produced by chemical vapor deposition technique in purity and microstructure.
The production of boron nitride by means of chemical vapor deposition is known to be carried out in the following manner. Boron-containing gas, for example, BCl.sub.3, BF.sub.3, or B.sub.2 H.sub.6, and nitrogen-containing gas, for example, NH.sub.3 or N.sub.2, are employed as source gases for depositing boron and nitrogen and these two kinds of the gases are allowed to react at a high temperature to form boron nitride. In this production process, if a solid substrate, such as graphite plate or metal rod, is present, boron nitride is deposited in a layered form onto the surface of the solid, thereby a thin film or massive deposit of boron nitride can be obtained. Since the boron nitride thus obtained by the chemical vapor deposition has a C-planes of crystallites of boron nitride orienting in parallel with the substrate, the properties are different between its depositing direction and the direction perpendicular to the depositing direction. Since the boron nitride by the chemical vapor deposition has the foregoing anisotropy in addition to the advantages, such as a high purity, a high corrosion resistance at an elevated temperature and superior electrical insulating property, it has become increasingly important as a unique material.
However, in the conventional vapor deposition method, for example, as disclosed in U.S. Pat. No. 3,152,006, a high density boron nitride can be deposited only at a high temperature of 1850.degree. to 2200.degree. C. For example, in the method of the aforesaid U.S. patent a boron nitride with a high density of 1.99 to 2.20 g/cm.sup.3 is not produced until the depositing temperature is elevated to 1850.degree. C. Thus, such a high temperature is indispensable for the deposition of boron nitride in the prior art and this fact is not only unfavolable from the standpoint of energy efficiency but also presents serious difficulties in enlargement of the production facilities and improvement of productivity. Under such circumstances, it is highly desirable to develop a new production method which makes possible the deposition of a high density boron nitride at lower temperatures.
Further, with respect to a massive body of boron nitride containing titanium, Japanese Patent publication No. 43-15078 discloses composite sintered bodies composed of titanium diboride and boron nitride. But boron nitride containing titanium nitride which is produced utilizing vapor deposition technique is not known up to date.